Nonflammable hydraulic fluid



Patented Feb. 22, 1949 UNITED STATES PATENT OFFICE NONFLAIVIMABLE HYDRAULIC FLUID No Drawing. Application October 9, 194.6, Serial No. 702,083

13 Claims. 1

This invention relates to fluid compositions for use in devices operated by fluid pressure, such as hydraulic brakes, clutches, shock absorbers, aircraft and ship control mechanisms, artillery recoil mechanisms, door checks, jacks and other such hydraulic devices adapted for transfer of mechanical energy.

This application is a continuation-in-part of my copending application Ser. No. 539,779, filed June 10, 1944, now Patent No. 2,455,961.

In the past it Was recognized that hydraulic fluids in general should be non-corrosive, nonfoaming, stable liquids which do not congeal at the low temperatures encountered in their use, and do not gasify at the elevated temperatures to which they may be subjected. It was also considered important that such compositions should not deteriorate rubber or other sealing materials with which they might come in contact, and also that they should have sufficient viscosity over a wide temperature range to permit smooth operation of the mechanism without danger of loss of the fluid.

The heretofore known fluids which possessed these desirable properties in even moderate degree were generally inflammable liquids which were not suited to use under conditions requiring high ignition temperature. However,. non-inflammability, as shown by high ignition temperature and other tests, is now recognized as being an important desirable property in such fluids, not only in warfare, but, more especially, in peacetime applications, such as commercial aviation. None of the heretofore commercially available hydraulic fluids were satisfactory in all of the characteristics now recognized as being desirable and important in such compositions for the prevention of accidents due to ignition of the said fluids.

An object o! the present invention is to provide a hydraulic fluid composition which is very difilcult to ignite under all types of conditions, and in addition has the other characteristics which are desirable in hydraulic fluids. Another object is to provide a process or method whereby the above-mentioned disadvantages of the previously known hydraulic devices can be overcome. A further object is to provide a composition which has a very low change of viscosity with temperature, and a suitable viscosity for use in hydraulic mechanisms over an unusually wide range of temperature. Still another object is to provide a composition which is a satisfactory lubricant for hydraulic apparatus and remains stable, noncorrosive, and relatively non-inflammable even after being subjected to the high shearing 2 stresses encountered in hydraulic systems containing high speed piston, gear or vane pumps, or other similar mechanisms.

These and other objects are accomplished in accordance with this invention by providing a composition containing water, a soluble thickener, and a compound selected from the group consisting of polyhydric alcohols and polyhydric alcohol ethers. The term "soluble thickener" as used in this specification refers to those thick eners which are soluble in water-polyhydric alcohol mixtures or in mixtures of water with polyhydric alcohol ethers. Generally such thickeners are of a resinous nature, and have molecular weights in excess of about 1000. Simple sugars and other simple crystalline compounds are not included as thickeners. In addition, there may be present in the composition a corrosion inhibitor. Suitable inhibitors include the alkali metal borates, phosphates, nitrites, phosphites and silicates; mercaptobenzothiazole and the like; amines such as morpholine, dimethylaminoethanol, diethylaminocthanol, triethanolamine, diethanolamine, monoethanolamlne, etc.; phosphates or other salts of the said amines; and similar commercially available inhibitors such as sodium borophosphate. Combinations of these inhibitors may be employed if desired, excellent results being obtainable with a corrosion inhibitor containing both diethylaminoethanol phosphate and mercaptobenzothiazole.

The polyhydric alcohols and polyhydric alcohol ethers include ethylene glycol, diethylene glycol, triethylene glycol, liquid polyethylene glycols, beta-hydroxyethy formal, monomethyl ether of ethylene glycol, monoethyl ether of ethylene glycol, monobutyl ether of ethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 2-methyl-l,3-pentanediol, 2-methyl-2,4- pentanediol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, glycerol, 1,3-butylene glycol, and other similar normally liquid polyhydric alcohols and polyhydric alcohol ethers. Of these, the preferred compounds in the practice of this invention are the polyhydric alcohols having 2 to 5 carbon atoms, especially ethylene glycol.

Suitable soluble thickeners include gum arable, gum ghatti, gum tragacanth, salts of cellulose glycolic acid, ethyl bromide addition products of either the polyvinyl pyridine or the styrene-vinyl pyridine co-polymers described in German Patent 695,098, polymerized alkylene ethers, such as polymers containing one or more of the following groups recurring at intervals:

etc; also the water-soluble derivatives of the synthetic linear polyamides; as a preferred group, the water-soluble synthetic resins including polyvinyl alcohol, salts of salt-forming acrylic resins (such as alkali metal polyacrylates and polyalkacrylates), and polymers of alkylene others may be employed if desired. The ethylene oxide polymers which are useful as thickeners include the polymers which are sold commercially under the name of Carbowax. The soluble polymers sold commercially under the name of Ucon also may be used. Ucon is a trade name for certain thickeners containing a polyalkylene ether structure.

Included among the soluble thickeners, for the purposes of the present invention, are watersoluble synthetic polyamide derivatives, particularly the alkali metal salts of N-(carboxyalkoxymethyl)-polyamides, which contain the recurring grouping methyl) derivatives form salts which can be used in accordance with the present invention include the polyamldes of the general type described in U. S. Patents 2,071,250, 2,071,253 and 2,130,948. Suitable polyamides are,i'or example,

poly hexamethylene adipamide, or the polyamides derived by reacting hexamethylene diamine or decamethylene diamine with sebacic acid or sebacic acid and ethylene glycol. It is not essention that all of the nitrogen atoms in the polyamide molecule be attached to -(carboxyalkoxymethyl) groups (or the salts thereof) although there should be a suflicient number of such groups per molecule to make the polymer soluble. The preferred potassium salts of N-(carboxymethoxymethyl) -hexamethylene polyadipamides are prepared by saponifying the methyl esters of N tcarboxymethoxymethyl) hexamethylene polyadipamides, which are obtained by the Cairns method mentioned above. These esters having saponification values in the range of about 100 to 160 (corresponding to about 38% t 100% substitution of the polyamide amido hydrogen by KOOCCHzOCHagroups) can be used as thickeners in accordance with this invention. For best results, the saponification value of the methyl ester from which this salt is made should be at least about 130. The phenol viscosi y of the ester is usually in the range of about 60 to 75. Phenol viscosity is the viscosity in centipoises at C, of a solution containing 5 grams of resin in 100 c. c. of an 85% phenol 45% water solution.

While the soluble thickeners are, as a class, generally applicable in accordance with this invention, it is frequently convenient to choose a particular soluble thickener to accomplish a specific task. Thus, for example, when the fluid is to be used in hydraulic systems containing mechanically driven pumps, the molecular weight of the thickening agent is important. Such systems exert a considerable shearing stress on the liquid, causing a permanent viscosity loss if the polymer has a high molecular weight and is subject to shear. Hence, a thickening agent of relatively low molecular weight, i, e.. less than 25,000, frequently about 5,000 to 10,000 would be chosen for this particular purpose. In general the soluble thickeners of this invention have molecular weights of at least 1,000, and for most applications of the invention the thickeners having a molecular weight of about 5,000 to 25,000 are preferred.

The range of proportions of the various constituents of the invention may vary widely. Good results, from the standpoint of lessened inflammability and other desirable properties, are obtained with a composition containing 0.2 to grams of the soluble resin per 100 c. c. of a base mixture containing 5% to 70% water, by volume, the remainder being a. compound selected from the group consisting of polyhydric alcohols and polyhydric alcohol ethers. The amount of thickener used depends upon the type and mol weight of the thickener, the fluid viscosity desired and the composition of the base fluid. About 0.1 to 5.0 grams of the corrosion inhibitor may also be added. The preferred corrosion inhibitor is borax. A suitable composition contains 2 to 30 grams of the resin (such as potassium polymethacrylate, solid ethylene oxide polymer or the potassium salt of N (carbomethoxymethyl) -po1yhexamethylene adipamide) per 100 c. c. of the base mixture which, in the preferred composition, is an aqueous ethylene glycol solution containing to 65% by volume of ethylene gycol, and about 1% by weight of borax.

The followin table lists several representative compositions which, in accordance with this in-. vention, have excellent hydraulic fluid properties and are very difiicult to ignite.

Table.-Properties of hydraulic fluid compositions Visoosity,0entistokes Viscosity Constituents of the Fluid g: :2 P

40 F. 0 F. 100 F. Slope 1 24.5 grams Carbowax "6000," 100 c. 0. base mixture containing 35 volume per cent ethylene glycol and 65 volume per cent water 333 27.1 0. 565 below -20 F. 2 1.0 gram potassium salt of polyacrylic acid, 1.0 gram sodium phosphate, 100 c. c. base mixture containing volume poi cent ethylene glycol and volume per cent water. 234 27. 3 0. 495 D0. .3 6.8 grams potassium saIt-oi polymethaci ylic acid, 100 c. 0. base mixture containing 45 volume per cent ethylene glycol and 55 volume per cent w or 276 26.9 0. 535 D0. 4 7 1 grams POlYVlIUl alcohol RH4i23 0.5 grams polyvinyl alcohol Bil-488 (made b Electrochcmicils Dept. of du Pont Co.) 1.0 grams hutyl phosphate, 0.5 gram BNOz. 100 c. 0. base mixture containing 45 volume per cent ethylene glycol and 55 volume per cent water 524 26.7 0. 647 Do. 5 1.53 grams potassium salt oi N-(corhoxymcihoxymetliyl)-polyhexamcthylene edipamide, L0 gram borax, 100 c. 0. base mixture containing ethylene glycol by volume and 40% water by volume 725 11. 76 0.600 below 00 F- sail-"- Tabla-Continued Viscoeit Oentistokes Viacosit Constituents oi the Fluid y tom ra Pour point tureurve 40 F. F. 100 F. Slope 1.0 grams potassium salt oi N-(carboxymethoxymetbyD-polyhexometh ylene adipemide, 1.0 gram borax, 100 c. e. of hose mixture containing 70% by volume diethylene glycol mono-ethyl ether and 307 by volume water 3,300 l3. 0 0. 770 below -00 F. 3.6 grams potassium salt oi polymethacryllc ac d, 2.0 gmmsoi tassium hosphate, 100 o. c. of base mixture containing 45% by volume ethy one glycol -lWZ, by volume water 200 29.7 0. 516 below F. 19.6 grams gum arable 100 c. c. of base mixture containing 45% by volume ethylene glycol -56? by volume water 428 20 0. 500 Do. 0.4 gram sodium carboxymetliyl cellulose sold commercially as Carccl N high viscosity grade, 1.0 gram borax, 100 c. c. of base mixture containing 45% by volume at ylene glycol 56% by volume water 234 27. 6 0. 494 below 0 F. 2.0 grams styrene-2-vinyl pyridine oopolymer ethyl bromide addition product. 100 c. c. base mixture containing 45% ethylene glycol by volume and 55% water by volume 142 0. 423 Do. 1! 2.5 grams polymerized 2-vinyl pyridine ethyl bromide addition product. 100 c.c.

base mixture containing 45% ethylene glycol by volume and 50% water by volume. 254 20. 0 0. 487 Do.

The hydraulic fluids of this invention have been used with outstanding success in the hydraulic systems of airplanes for the operation of mechanisms which are normally actuated by hydraulic fluids, such as landing gear, etc.

Moreover the lnflammability of these fluids has been tested for by various methods such as (1) spontaneous ignition temperature, (2) flash point, (3) percentage of oxygen in nitrogen required to burn the atomized fluid under controlled conditions, and (4) ignition by incendiary bullets, and by all of these tests the fluids described in the Table are either non-inflammable, or are very much less inflammable than the customary, commercial hydraulic fluid compositions. The spontaneous ignition temperatures of the hydraulic fluids of this invention are in most instances remarkably high, e. g. generally at least about 850 to 900 F.

Since many apparently different embodiments of the present invention may be made without departing from the spirit and scope thereof, it will be understood that we do not limit ourselves except as set forth in the appended claims,

I claim:

1. A hydraulic fluid consisting essentially of water, a polyhydric alcohol havingfrom 2 to 5 carbon atoms per molecule, and, as a soluble thickener, from 0.2 to grams of a polymerized alkylene ether having a. molecular weight in excess of about 1000 and having recurring alkylene groups containing from 2 to 4 carbon atoms, per 100 c. c. of the said mixed water and polyhydric alcohol. the principal ingredient of the said fluid be ng the said polyhydric alcohol.

2. A hydraulic fluid consisting essentially of water, a polyhydric alcohol having from 2 to 5 carbon atoms per molecule, a corrosion inhibitor,

' and, as a soluble thickener, about 0.2 to 30 grams of a polymerized alkylene ether per 100 c. c. of the said mixed water and polyhydric alcohol, the principal ingredient of the said fluid being the said polyhydric alcohol, said polymerized alkylone other having a molecular weight in excess of 1000 and having recurring alkylene groups containing from 2 to 4 carbon atoms.

3. The composition set forth in claim 2 in which the said corrosion inhibitor is borax.

4. The composition set forth in claim 2 in which the said corrosion inhibitor is a mixture of diethylaminoethanol phosphate and mercaptobenzothiazole.

5. The composition set forth in claim 2 in water, ethylene glycol, and, as a. soluble thickener, from 0.2 to 30 grams of a. polymerized alkylene'ether having a molecular weight in excess of about 1000, per 100 c. c. of the said mixed water and ethylene glycol, the principal ingredient of the said fluid being ethylene glycol, said polymerized alkylene ether having recurring alkylene groups containing from 2 to 4 carbon atoms.

'7. A hydraulic fluid consisting essentially of water, ethylene glycol, a corrosion inhibitor, and, as a soluble thickener, about 0.2 to 30 grams of a polymerized alkylene ether per 100 c. c. of the said mixed water and ethylene glycol, the principal ingredient of the said fluid being ethylene glycol, said polymerized alkylene ether having a molecular weight in excess of about 1000 and having recurring alkylene groups containing 2 to 4 carbon atoms.

8. The composition set forth in claim '7 in which the said corrosion inhibitor is borax.

9. The composition set forth in claim 'I in which the said corrosion inhibitor is a mixture of diethylaminoethanol phosphate and mercaptobenzothiazole.

10. The composition set forth in claim '1 in which the said inhibitor is an alkali metal phosphate.

11. A hydraulic fluid composition consisting essentially of 0.2 to 30 grams of a soluble thickener of molecular weight in excess of about 1000, and 0.1 to 5.0 grams of a corrosion inhibitor per 100 c. c. of a base solution consisting essentially of water and from 30 to by volume of ethylene glycol, said soluble thickener being a polymerized alkylene ether and having recurring allrylene groups containing from 2 to 4 carbon atoms.

12. The process which consists essentially in actuating a hydraulic mechanism by means of a hydraulic fluid consisting essentially of water, a normally liquid polyhydric alcohol, and, as a soluble thickener, from 0.2 to 30 grams of polymerized alkylene ether having a molecular weight in excess of about 1000 and having recurring alkylene groups containing from 2 to 4 carbon atoms, per c. c. of the said mixed water and polyhydric alcohol, the principal ingredient of the said fluid being the said polyhydric alcohol-water mixture.

13. The process which consists essentially in actuating a hydraulic mechanism with a hydraulic fluid consisting essentially of water, ethylene glycol, a corrosion inhibitor, and, as a soluble thickener, from 0.2 to 30 grams of a polymerized alkylene ether having a molecular weight in excess of about 1000 and having recurring alkylene groups containing from 2 to 4 carbon atoms, per 100 c. c. o! the said mixed water and REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date Campbell May 31, 192! Cox Feb. 26, 1935 Paxton Nov. 10, 1936 Winning et a1. Feb. 23, 1937 Downing July 13, 193'! Bayes Feb. 14, 1939 

